The present invention relates to a communication line surge protecting system that protects a communication line, communication equipment, or the like from lighting surge and the like induced in the communication line.
Efforts have hitherto been made to protect a communication line, connection equipment, or the like from damage caused by lighting surge and the like induced in the communication line. In this conventional lighting surge protecting system, a lighting arrester such as a gas tube arrester is disposed between an outer circumference of a central conductor of a coaxial connector and an inner circumference of an external conductor. Thus, lighting surge and the like induced in the communication line are discharged and grounded by the lighting arrester to protect the communication line, connection equipment, or the like from lighting surge and the like.
However, in the above described conventional lighting surge protecting system, a temporal delay in operation occurs after lighting surge and the like have invaded into the communication line and before the lighting arrester performs a discharge operation. As a result, lighting surge associated with the temporal delay in operation of the lighting arrester may invade into the communication line or connection equipment, thereby disadvantageously damaging the connection equipment or the like.
Further, since the lighting arrester is connected between the outer circumference of the central conductor of the coaxial line and the inner circumference of the external conductor, a capacity is added to this portion to disadvantageously increase losses to the communication line, thereby narrowing a frequency band.
It is an object of the present invention to solve the problems with the above described conventional lighting surge protecting system and to provide a communication line surge protecting system which allows, for a communication line, a signal with a predetermined frequency to pass therethrough, while blocking signals with the frequency components of lighting surge and the like and which allows, for the ground, the signals with the frequency components of lighting surge and the like to pass therethrough for grounding, while blocking the signal with the predetermined frequency.
To accomplish the above object, first, a quarter wavelength open circuit for a wavelength used is disposed in each of a central conductor line 1 and an external conductor line 2 so as to allow a signal with a predetermined communication wavelength to pass therethrough, while blocking signals with frequency components of lighting surge and the like, and in which a ground line is further provided in the central conductor line and a quarter wavelength short circuit for the wavelength used is disposed in each of the ground line and the external conductor line so as to block the signal with the predetermined communication wavelength, while allowing the signals with the frequency components of lighting surge and the like to pass therethrough for grounding. Second, the quarter wavelength open circuit for the wavelength used is constructed by interposing an insulator with a length one fourth of the wavelength used, into each of the central conductor line and the external conductor line. Third, the quarter wavelength open circuit for the wavelength used is constructed by dividing each of the central conductor line and the external conductor line into pieces and interposing an insulator between the pieces of each of the central conductor line and the external conductor line.